The actuator device is formed of an actuator motor alone or is modularized with a peripheral circuit, wiring, a connector, an attachment frame and the like. It is possible to realize a simple mechanism, a reduced cost, reduction in types of parts, and improved maintainability by using the same actuator devices in a plurality of sites in the multi-shaft driving mechanism such as the multi-shaft manipulator, the robot arm, the leg structure, and the snake-shaped robot. For example, a manipulator of an industrial robot formed of same modular driving devices is suggested (refer to Patent Document 1, for example).
A substantial outer shape of the modularized actuator device is a cylinder (refer to Patent Document 2, for example), a cuboid, combination of the cylinder and cuboid (semicylinder) (refer to Patent Document 3, for example), an oval sphere and the like.
In the multi-shaft driving mechanism, a structure in which another actuator is attached to an output shaft of the actuator is common. FIG. 18 illustrates a configuration example of the multi-shaft driving mechanism in which a second actuator is attached to the output shaft of a first actuator such that the output shafts thereof are orthogonal to each other and a frame is attached to the output shaft of the second actuator. In the multi-shaft driving mechanism, the first actuator and the second actuator correspond to a preceding stage and a subsequent stage, respectively. According to the illustrated mechanism, a posture (a direction of the output shaft) of the second actuator changes by rotary drive of the output shaft of the first actuator and the frame rotates about the output shaft of the second actuator to change a posture.
In a case of the multi-shaft driving mechanism illustrated in FIG. 18, a substantial occupied space of the second actuator is a space formed by a rotating body with an outermost diameter including the second actuator and the frame as illustrated in FIG. 19. In other words, when the second actuator is rotated by the first actuator, the occupied space thereof depends on shapes of the frame attached to the output shaft of the second actuator and an end of the second actuator, and the substantial occupied space is larger than an original volume of the second actuator. It may also be said that the occupied space increases when the frame is attached to the second actuator.
When the substantial occupied space of the actuator becomes large, possibility of interference with the surroundings increases correspondingly and a risk that user's finger, wiring and the like get caught therein arises. A spherical exterior (cover) may be arranged, for example, on an outer side of the driving mechanism in order to avoid such risk. However, a structure body covered with the exterior has a wasted space (vacuum or containing only air) not for an original object of the actuator (parts, torque generation, torque conversion and the like) in the driving mechanism, so that output density of the actuator device and mounting density of the parts are deteriorated. As a result, this makes a multi-joint robot formed of the actuator devices used in a plurality of sites large and limits a range in which an entire multi-joint robot may move and an operable range thereof, or reduces a range of motion of each joint.